Too massive to be classified as planets but too light to sustain hydrogen fusion like stars, these “failed stars” emit only faint heat and light. Brown dwarfs offer valuable insights into both stellar and planetary formation, as well as the conditions that exist at the boundary between the two.
1. Gliese 229B
Location: Constellation Lepus | Distance: ~19 light-years
Gliese 229B was the first confirmed brown dwarf, discovered in 1995. Orbiting a red dwarf star, it was one of the earliest objects identified to contain methane in its atmosphere—similar to gas giants like Jupiter. This detection confirmed that Gliese 229B was too cool and low in mass to be a star, solidifying the brown dwarf category and establishing new benchmarks for studying substellar objects.
2. WISE 0855–0714
Location: Hydra | Distance: ~7.2 light-years
Discovered by the Wide-field Infrared Survey Explorer (WISE) in 2014, WISE 0855–0714 is one of the coldest known brown dwarfs, with temperatures around −23°C. This makes it remarkably similar to gas giants in our solar system. The study of its atmosphere—likely containing water clouds—has brought us closer to understanding how planetary atmospheres form and evolve.
3. Luhman 16A and 16B
Location: Vela | Distance: ~6.5 light-years
Luhman 16 is a binary system containing two brown dwarfs, making it one of the closest such systems to Earth. Discovered in 2013, the two objects orbit each other in a cosmic dance that has allowed astronomers to precisely measure their masses and temperatures. Observations suggest that Luhman 16B may have patchy cloud systems, offering a rare glimpse into the dynamic weather on brown dwarfs.
4. 2MASS J22282889-431026
Location: Grus | Distance: ~115 light-years
2MASS J22282889-431026 is notable for its erratic weather patterns. This brown dwarf exhibits dramatic brightness variations, thought to be caused by massive cloud systems rotating in and out of view. Its fast-changing atmosphere makes it an ideal candidate for studying the weather cycles on brown dwarfs and comparing them to those of gas giant planets.
5. SDSS J0104+1535
Location: Pisces | Distance: ~750 light-years
SDSS J0104+1535 is one of the oldest brown dwarfs ever detected, estimated to be over 10 billion years old. It contains very low metallicity, meaning it has few elements heavier than hydrogen and helium. This suggests it formed during a much earlier period in the universe’s history, offering insights into how substellar objects formed in environments with minimal heavy elements.
6. WISE 1217+1626 AB
Location: Ursa Major | Distance: ~34 light-years
WISE 1217+1626 is another binary brown dwarf system, with one of the objects being an exceptionally cool “Y-dwarf.” Y-dwarfs represent the coldest category of brown dwarfs, with temperatures barely above that of Earth’s atmosphere. Observations of WISE 1217+1626 have helped refine the classification of brown dwarfs into spectral types, stretching our understanding of the transition between stars and planets.
7. SIMP J01365663+0933473
Location: Pisces | Distance: ~20 light-years
This brown dwarf surprised astronomers when it was found to have a powerful magnetic field and auroras, similar to those observed on Jupiter. The detection of radio emissions from SIMP J01365663+0933473 challenges the idea that auroras are restricted to planets, hinting at a possible connection between planetary magnetism and that of brown dwarfs.
Brown dwarfs are cosmic hybrids, embodying traits of both stars and planets. Their study has expanded our understanding of substellar objects, planetary formation, and atmospheric behavior. From dynamic weather systems to magnetic fields and ancient compositions, brown dwarfs continue to blur the lines between celestial categories, challenging astronomers to rethink the definitions of stars and planets.